Two-plane balance for spindle motors

ABSTRACT

In a spindle hub configured for rotation about an axis, through holes extend from a first end of the spindle hub to a second end of the spindle hub. The through holes are generally parallel to the axis. A method of achieving two-plane balance of a disc pack assembly by positioning one or more weights in one or more of the through holes and retaining the weight in the position, such that it is possible to access each weight from the top of the spindle hub.

This patent application claims priority from U.S. ProvisionalApplication No. 60/136,577, filed May 28, 1999.

FIELD OF INVENTION

The present invention relates generally to spindle motor assemblies indisc drives, and more particularly to the balancing of disc packassemblies.

BACKGROUND OF THE INVENTION

In a disc drive, a spindle motor assembly comprises a stationary portionand a rotary portion. The rotary portion, also referred to as the discpack assembly, typically includes a number of discs and spacers mountedon a spindle hub. As the disc pack assembly is rotated, the lack ofperfect symmetry about the axis of rotation results in vibration of thedisc pack assembly. Therefore, it is necessary to balance the disc packassembly.

For ease of reference, the end of the spindle hub which is mountednearer a spindle base flange in the disc drive will be referred to asthe bottom end, and the opposite end of the spindle hub will be referredto as the top end.

One method of balancing a disc pack assembly is described in the U.S.Pat. No. 5,555,144 issued Sep. 10, 1996, to Wood, et al. for “BalancingSystem for a Disc Drive Disc Assembly”. This method involves mounting aC-shaped balancing clip to the disc pack assembly such that, byselecting a balancing clip with an appropriately located center of massand selecting an appropriate orientation for the balancing clip, thedisc pack assembly can be balanced.

To achieve two-plane balance, the balance at the top end and at thebottom end of the disc pack assembly are separately adjusted by mountingbalancing clips to both the top and the bottom ends of the spindle hub.In the case of an “under-hub” spindle motor assembly, the bottom enddoes not provide access for the balancing clips to be mounted because ofthe way the motor magnet and the stator are arranged below the spindlehub flange.

Another approach to balancing is described in the U.S. Pat. No.5,621,588 issued Apr. 15, 1997 to Williams, et al. for “Two-PlaneBalance for Hard Disk Drive Motor-Base Assemblies.” According to thismethod, a set of balancing screws are fastened to a top surface of thespindle hub, and another set of balancing screws are fastened to abottom surface of the spindle hub. The spindle motor assembly is mountedon a base plate by means of mounting screws. The mounting screws arechosen to be larger than the balancing screws in order that the bottomsurface of the spindle hub can be accessed from the bottom direction byremoving a mounting screw.

Thus, it has been generally inconvenient and difficult to adjust thebottom-plane balance of a disc pack assembly. Therefore, there remains aneed for an improved method of balancing a disc pack assembly. It willbe evident from the following description that the present inventionoffers this and other advantages over the prior art.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a spindlehub configured for rotation about an axis. The spindle hub has aplurality of through holes on the spindle hub. The through holes extendfrom a first end of the spindle hub to a second end of the spindle hub,in a direction generally parallel to the axis.

A weight and a through hole on the spindle hub are configured such thatthe weight can be inserted into the through hole from the top of thespindle hub.

In one embodiment, the weight can be fixed at different positions insidethe through hole.

In another embodiment, the through hole includes a stop at the secondend of the spindle hub. A retainer is configured to retain the weight ina position between the retainer and the stop.

According to another aspect of the invention, there is provided a methodof balancing a disc pack assembly. The method includes providing aspindle hub having a plurality of through holes extending from a firstend to a second end of the spindle hub in a direction generally parallelto the axis. The method also includes a step of positioning a weightwithin one of the through holes.

The method may further include a step of retaining the weight in aposition within the through hole.

The present invention therefore provides for an improved method ofachieving two-plane balance in a disc pack assembly. The invention alsoprovides an easier way of adjusting the bottom-plane balance. Inaddition, it facilitates the implementation of a more efficientmanufacturing system as it does not require robots to access the discpack assembly from both the top and bottom directions.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an exploded view of a disc drive.

FIG. 2 is a cross-section showing a preferred embodiment of theinvention as applied to an “under-hub” spindle motor assembly.

FIG. 3 is a flowchart showing a method of balancing a disc pack assemblyaccording to one embodiment of the invention.

FIG. 4 is a top view of a clamp ring.

FIG. 5 shows an example of a nylock-type screw.

FIG. 6 shows further embodiments of the invention as applied to an“in-hub” spindle motor assembly.

FIG. 7 is a cross-section of a spindle motor showing an extended throughhole.

DETAILED DESCRIPTION

FIG. 1 is an exploded view of a disc drive 11 with a deck 12 between atop cover 13 and a controller board 15. Discs 22 are shown in assemblywith a clamp ring 26. The discs 22 are mounted on a spindle hub 20 whichis hidden from view below the clamp ring 26.

As a preferred embodiment of the invention is described with referenceto FIG. 2, it can be seen that the present invention allows a spindlemotor assembly to be assembled from the bottom up, with a robotaccessing the assembly from only the top direction.

The spindle base flange 10 is first mounted to the deck 12 of the discdrive 11. Stator 14 and magnet 16 are located about a shaft 18 of thespindle motor, above the spindle base flange 10. The magnet 16 andback-iron 17 are attached to a spindle hub 20 which is assembled to therest of the spindle motor such that it is free to rotate about the shaft18 through the bearing means 19.

A series of discs 22 are loaded, from the top, onto the spindle hub 20.The discs 22 are typically interspersed by spacers (not shown) andsecured to the spindle hub 20 by some mounting device so that the discs22 rotate with the spindle hub 20 about the shaft 18 when the disc driveis in operation.

In conventional systems, the bottom-plane balance of the disc pack isdifficult to adjust because the arrangement of the spindle base flange10 does not provide easy access to the spindle hub flange 24 for balanceweight access. It can be seen from the FIG. 2 that it would be difficultto put in place a C-shaped balancing clip at the spindle hub flange 24from either the side or the top of the disc pack assembly.

A clamp ring 26 is fitted at the top end of the spindle hub 20 such thatit holds down the discs 22. The clamp ring 26 usually has six firstclamp ring holes 28 which correspond to six clamp ring screw holes 30 onthe top surface of the spindle hub 20 so that the clamp ring 26 can besecured to the spindle hub 20 by means of six clamp ring screws 32.

According to a preferred embodiment of the present invention, a throughhole 36 is located in the spindle hub 20 such that it extends from a topsurface of the spindle hub 20 to a bottom surface of the spindle hub 20.For illustrative purposes only, the FIG. 2 shows one arrangement of thethrough holes 36 in an “under-hub” spindle motor. Other possiblearrangements of the through holes 36 are shown in the context of an“in-hub” spindle motor in FIG. 6.

Preferably, through holes 36 are situated in the spindle hub 20 so thatthe spindle hub 20 has rotational symmetry about an axis 38 of the shaft18. In a most preferred embodiment, six through holes 36 are situated onthe hub 20 between the clamp ring screw holes 30 such that they areequidistant from one another. A corresponding second clamp ring hole 39may be required in the clamp ring 26 if the through hole 36 is arrangedsuch that it is covered by the clamp ring 26 when the disc pack assemblyis completed. FIG. 4 shows a top view of such a clamp ring 26 with onearrangement of the first clamp ring holes 28 and the second set ofclearance clamp ring holes 39, constructed to correspond to the clampring screw holes 30 and the through hole 36, respectively. The samefigure also provides an indication of one arrangement of the throughholes 36, relative to the clamp ring screw holes 30, on the spindle hub20.

A weight 40 is configured such that it can be inserted into one of thethrough holes 36 from the top of the spindle hub 20 and be moved fromthe top of the spindle hub 20 along the through hole 36 to the bottom ofthe spindle hub 20.

Making reference to FIG. 3, the procedure for balancing starts 50 afterthe disc pack is assembled 52 onto the stationary portion of the spindlemotor. The disk pack assembly is then checked for imbalance 54. If thedisc pack assembly is not balanced, a computer can be used to determinewhere one or more weights 40 and/or 42 should be positioned. Therequired weights 40 are then inserted into the appropriate through holes36 and moved to the desired position 56. The balance of the disc packassembly may be verified 54 before the procedure is ended 58 when thedesired degree of balance has been achieved. The steps of checking theimbalance 54 and of positioning appropriate weights 56 can be repeated,if so desired.

Because each weight 40 can be positioned anywhere along the length of athrough hole 36, the balance of the disc pack assembly can be changed insmaller steps. This embodiment of the present invention therefore has anadditional advantage of improving the degree to which the balance can befine-tuned. Furthermore, it also allows for a closer match to thedesired degree of balance in a single round of balancing.

Another advantage of this embodiment is that the balance of the discpack assembly in both the top-plane and the bottom-plane can be adjustedby changing the position of the weight 40 in the through hole 36. Withthe aid of a computer which identifies where a weight 40 shouldpreferably be positioned in a through hole 36, the disc pack assemblycan be balanced in a single positioning step 56.

In a preferred embodiment of the invention, the through holes 36 and theweights 40 are threaded so that each weight 40 can be made to travelalong the length of the through hole 36 by means of a torx driver, analien driver or other such like tool.

Preferably, the weight 40 is configured such that it will not changeposition after the desired balance is achieved. One preferred embodimentuses nylock-type screws for the weights 40. One example of a nylock-typescrew is illustrated schematically in FIG. 5. It is shaped like asetscrew with an external thread 70 chosen to correspond with aninternal thread of the through hole 36. A piece of elastic material 72resides in a cavity 74 such that part of the elastic material 72protrudes out from the threads of the screw. The top end of thenylock-type screw has features 76 to allow for engagement by a torxdriver, an alien driver or other such like tool. When the nylock-typescrew is not being threaded along the through hole 36, the elasticmaterial 72 holds the nylock-type screw securely fitted in the throughhole 36.

Further embodiments of the present invention are illustrated in FIG. 6.Referring to the right-hand half of the figure, the weight 40 may be aball or cylinder of steel, lead, tungsten or other suitable materials,configured for interference fit with the through hole 36. If acylindrical shape is used, the cylinder may be constructed of differentlengths as required to achieve the desired balance. The weight 40 inthis case can be pushed as near the bottom of the through hole 36 asdesired, and it will remain in that position even when the disc drive 11is in operation.

In yet another embodiment of the invention, which can also beillustrated by the right-hand half of FIG. 6, the weight 40 isconfigured for loose fit with the through hole 36. A robot can beprogrammed and arranged to access the through hole 36 from the top ofthe spindle hub 20 and move the weight 40 in either direction inside thethrough hole 36. Glue can be applied to the weight 40 to secure it in adesired final position.

In another example, the disc pack assembly may be fitted with a weight40 in each of the through holes 36 such that all the weights 40 are atthe bottom of the spindle hub 20 at the beginning of the balancingprocedure. To adjust the balance, one or more of the weights areaccessed from the top of the spindle hub 20 and moved away from thebottom of the spindle hub 20. Preferably, the weights 40 are nevercompletely removed from the hub 20 so as to reduce the possibility ofaccidentally dropping a weight 40 and damaging the discs 22. The initialpositions of the weights can, of course, vary from this example withoutgoing beyond the scope of the invention.

The left-hand half of FIG. 6 shows an alternative embodiment of thepresent invention where the through hole 36 includes a stop 60 at thebottom end of the spindle hub. A weight 40 which is configured for loosefit with the through hole 36 can be inserted into the through hole 36from the top of the spindle hub 20. The stop 60 may be formed as aconstriction or a tab which will prevent the weight 40 from moving outof the through hole 36 at the bottom end of the spindle hub 20.

A retainer 62 can be used to retain the weight 40 at the bottom of thethrough hole 36. A suitable retainer 62 is likely to be much lighterthan the weight 40 so as not to influence the balance of the disc packassembly. One example of a retainer 62 is molded from a resilientmaterial and sized a little larger than the through hole 36 such thatwhen it is inserted into the through hole 36, a press fit is createdbetween the retainer 62 and the through hole 36. A retainer 62 can beshaped like a cylinder, or preferably it may have a square profile or awavy profile so that it is easier to fit into the through hole 36.

In another embodiment, the retainer 62 may include an internallythreaded hole 64 by which the retainer 62 can be secured by a tool andremoved from the through hole 36. The weight 40 can then be dumped outof the through hole 36 and the disc pack can be sent for rework.Preferably, the internally threaded hole 64 is tapered.

Alternatively, as shown in FIG. 7, the through hole 36 is extendedthrough the back-iron 17 and the spindle base flange 10. The extendedhole 36′ allows a rod to be inserted from the bottom direction such thatthe weight and retainer, if any, are pushed up and out of the spindlehub 20 if removal of the weight becomes necessary, for example, in thecase of rework.

A person skilled in the art will understand that the present inventioncan be applied in different ways without going beyond the scope of theinvention. For example, as shown in FIG. 2, one embodiment of thepresent invention also allows for a C-shaped balancing clip 42 to befitted to the clamp ring 26 to provide some adjustment of the top-planebalance, if so desired.

The present invention is not limited to the case where one weight 40 islocated in each through hole 36. According to the adjustments requiredto achieve the desired balance, more weights 40 can be added to onethrough hole 36, as shown in FIG. 7, or a particular through hole 36 maynot need to have a weight 40 in it.

The person skilled in the art will also understand that the size andnumber of through holes 36 as well as the dimensions of the weights 40can also be varied without going beyond the scope of the presentinvention.

As mentioned in the foregoing, a computer can be programmed to determinethe top-plane and bottom-plane balance of the hub assembly so that eachweight 40 can be moved to an appropriate position and the desiredbalance can be achieved quickly. This however, does not preclude thesituation where an operator adjusts the balance manually.

Various embodiments of the present invention are further describedbelow.

A spindle hub 20 is configured for rotation about an axis 38. Thespindle hub 20 includes a first end and a second end. The spindle hub 20also includes through holes 36 such that the through holes 36 extendfrom the first end to the second end in a direction generally parallelto the axis 38.

The spindle hub 20 may further include a weight 40 inside one of thethrough holes 36. The weight 40 and the through hole 36 are configuredsuch that the weight 40 can be fixed at different positions along thethrough hole 36.

In one embodiment, the weight 40 and the through hole 36 are configuredfor interference fit with each other.

In another embodiment, the weight 40 has an external thread cooperativewith the internal thread of the through hole 36.

In one embodiment, the weight is a nylock-type screw.

In another embodiment, the through hole 36 includes a stop 60 at thesecond end of the spindle hub 20.

The weight 40 may be positioned in the through hole 36 at the stop 60.

In one embodiment, the weight 40 is retained in a position between aretainer 62 and the stop 60.

The retainer 62 and the through hole 36 may be configured for press fitwith each other.

The retainer 62 may further include an internally threaded hole 64 suchthat when the retainer 62 is inside the through hole 36, the internallythreaded hole 64 is accessible from the first end of the spindle hub 20.

The through holes 36 may be positioned on the spindle hub such that theyare equidistant from one another.

A method of balancing a disc pact assembly which includes providing aspindle hub 20 as described above, and positioning a weight 40 withinone of the through holes 36.

The positioning step may be carried out by accessing the weight fromonly the first end of the spindle hub.

The method may further include a step of retaining the weight 40 in aposition within the through hole 36.

The method of retaining the weight may be carried out by accessing thedisc pack assembly from only the first end of the spindle hub.

In one embodiment, the method includes a step of determining theimbalance of the disc pack assembly.

The method performed such that two-plane balance of the disc packassembly is achieved.

Therefore, it can be understood that the present invention makes itpossible for two-plane balance of an assembly to be adjusted withoutrequiring access from both the top and bottom directions of theassembly. It follows that the invention offers an improved method ofadjusting the two-plane balance of an assembly, especially when there issome difficulty gaining access to the bottom of the assembly. It alsooffers other advantages by reducing constraints in the method ofmanufacturing the assembly, for example, by making it possible toassemble and balance the assembly while gaining access to the assemblyfrom only one direction.

The foregoing description is only illustrative of various embodiments ofthe invention, and a person skilled in the art will understand thatchanges can be made to the details of structure function and processeswithout going beyond the scope of the present invention.

1-18. (canceled)
 19. A method of balancing a disc pack assembly of adisc drive, the disc pack being configured to rotate about an axis, themethod comprising steps of: (a) providing a spindle hub having aplurality of through holes each extending from a top surface of the hubsubstantially to a lowest surface of the hub in a direction generallyparallel to the axis; and (b) positioning at least one weight within atleast one of the plurality of through holes.
 20. A method according toclaim 19 wherein the positioning step (b) is carried out by accessingthe weight from only the top surface of the spindle hub.
 21. A methodaccording to claim 19 further comprising a step (c) of retaining the atleast one weight in a position within the at least one through hole. 22.A method according to claim 21 wherein the retaining step (c) is carriedout by accessing the disc pack assembly from only the top surface of thespindle hub.
 23. A method according to claim 19 further comprising astep (c) of determining imbalance of the disc pack assembly.
 24. Amethod according to claim 19 wherein the providing step (a) and thepositioning step (b) are performed to achieve two-plane balance of thedisc pack assembly.
 25. (canceled)
 26. A method according to claim 21wherein retaining the at least one weight in a position within the atleast one through hole includes retaining by providing an interferencefit between the at least one weight and the at least one through hole.27. A method according to claim 21 wherein retaining the at least oneweight in a position within the at least one through hole includesretaining by providing internal threads on a surface of the at least onethrough hole and engaging complementary external threads formed on theat least one weight.
 28. A method according to claim 21 whereinretaining the at least one weight in a position within the at least onethrough hole includes retaining by providing an adhesive to further fixthe at least one weight within the at least one through hole.
 29. Amethod according to claim 21 wherein retaining the at least one weightin a position within the at least one through hole includes retaining byproviding a weight configured as a cylinder and having a cylindricalaxis that is generally parallel to the axis of the spindle hub.
 30. Amethod according to claim 29 further including a step of selecting alength of the cylindrical axis to balance the spindle hub.
 31. A methodaccording to claim 29 further including a step of positioning the atleast one weight at an axial position within the at least one throughhole so as to balance the spindle hub.